The present invention relates to a synchronizing system, and more particularly relates to means used between two devices transmitting data at different speeds to counteract this differential as a buffer.
In any circuit interfacing two non-correlated and asynchronous clocks, there will exist a non-zero probability of sampling a signal from one system with the clock from the other system while the signal is changing. The result of such a sampling, where set-up and hold times are not met, may be an erroneous output. Unpredictably the output can be logic "1", logic "0" or in a "metastable state" between "1" and "0". This undefined logic state may be interpreted differently by different receiving devices, and in a general configuration it is able to propagate through the succeeding logic gates.
This "metastable state" is discussed in the articles, "General Theory of Metastable Operation" by Leonard R. Marino, P107-P115, IEEE TRANSACTIONS ON COMPUTERS, Vol. C.30, NO.2, February, 1981, "Anomalous Behavior of Synchronizer and Arbiter Circuits" by Thomas J. Chaney et al, P421-P422, IEEE TRANSACTIONS ON COMPUTERS, Correspondence, April, 1973, and "Circuit Technology in a large computer system" by D. J. Kinniment et al, P435-P441, THE RADIO AND ELECTRONIC ENGINEER, Vol. 43, No.7, July, 1973. The metastable state is potentially unstable and the probability that the output will stay in metastable state decays exponentially with time. All logic families exhibit the metastable operation, when sampling occurs on a transition. However, families with a high-gain bandwidth product are less inclined to exhibit the metastable state than those with a low-gain bandwidth product. The metastable problem is a fundamental problem in digital circuits interfacing asynchronous clocks, and there exists no exact solution to avoid errors. However, the probability of inducing errors due to the metastable operation can be reduced by allowing longer time for the output to settle from the metastable state and by employing high-gain bandwidth product devices.